Quick fix get the ohms per inch for your wire and just wrap till you have about 1/4" dir each leg. Even when changing mandrel sizes your resistance should be constant for the most part.
Here's my quick list:
24 ga: .185 ohms/in
26 ga: .295 ohms/in
28 ga: .512 ohms/in
30 ga: .725 ohms/in
32 ga: .1.15 ohms/in
I will play with mandrel sizes and report back with only changing that element but you also may want to check with super_x in the other micro coil thread and see if he has the info.
And a link to super_x in the other thread: http://www.e-cigarette-forum.com/for...php?p=12395285